1. Field of Invention
This invention relates to a solenoid valve which can be used for example, in a vehicle to control brake fluid pressure by opening or closing the various brake lines.
2. Description of Prior Art
This type of solenoid valve has been used in an anti-locking braking system (ABS) or traction control system (TCS) of an automobile. For that purpose, the solenoid valve fitted in a valve block, which is comprised of several normally open solenoid valves and normally closed solenoid valves, a hydraulic pump, and a pressure chamber. FIG. 11 illustrates a normally closed solenoid valve a incorporated into a valve block.
In this configuration, a mounting block b is used to mount several solenoid valves a. On one side of said mounting block b several housing cavities c, each of non-uniform diameter over the length of the cavity are bored at prescribed intervals, wherein brake fluid lines drilled through the mounting block b pass between the housing cavities.
Solenoid valve a is configured from an energizing coil d, a case e which houses said energizing coil d, and a plunger h housed in the center of the case. Valve seat l is positioned in the center on the bottom of the case e. Plunger h is a selector valve comprised of a valve head i molded on its tip and the valve seat l.
When coil d is de-energized, valve head i remains seated in valve seat i by the spring force of the spring n compressed between plunger h and yoke ring m which blocks passage through port 1 j and port 2 k; when coil d is energized, an energizing force in the direction to compress spring n acts upon plunger h, wherein valve head i separates from valve seat i to open passage between the two ports j and k.
Seal t and seal g are fitted around the lower segment of the case e to ensure an airtight seal of the solenoid valve a in the lower recess of housing cavity c.
With a solenoid valve a of this type, should pressure be generated at port 2 k when the valve arrangement is closed, the said pessure acts in the direction to lift solenoid valve a out of housing cavity c. This separation force is generated by the following mechanism.
Setting the pressure-subjected area of seal t as A1, the pressure-subjected area of seal g as A2, and the pressure of port k as P, then the pressure acting upon seal f is the product of the area A1 multiplied by pressure P(A1.times.P) and the pressure acting upon seal g is the product of the area A2 multiplied by pressure P(A2.times.P).
Accordingly, a separation force equal to the difference between the two pressures [(A1.times.P)-(A2.times.P)] is generated. This separation force becomes proportionally larger the greater the difference between the pressure-subjected areas of seal t and seal g at each position.
A steel plate or other high-strength pressure plate o is positioned on the outside of the yoke ring m to press against valve a to resist the force in the axial direction (axial force) caused by this pressure.